refactor(examples): switch examples from cra to nextjs

examples/nextjs/pages/DragNDrop/Sidebar.tsx

@@ -0,0 +1,40 @@
+import React, { DragEvent } from 'react';
+import styles from './dnd.module.css';
+
+const onDragStart = (event: DragEvent, nodeType: string) => {
+  event.dataTransfer.setData('application/reactflow', nodeType);
+  event.dataTransfer.effectAllowed = 'move';
+};
+
+const Sidebar = () => {
+  return (
+    <aside className={styles.aside}>
+      <div className={styles.description}>
+        You can drag these nodes to the pane on the left.
+      </div>
+      <div
+        className='react-flow__node-input'
+        onDragStart={(event: DragEvent) => onDragStart(event, 'input')}
+        draggable
+      >
+        Input Node
+      </div>
+      <div
+        className='react-flow__node-default'
+        onDragStart={(event: DragEvent) => onDragStart(event, 'default')}
+        draggable
+      >
+        Default Node
+      </div>
+      <div
+        className='react-flow__node-output'
+        onDragStart={(event: DragEvent) => onDragStart(event, 'output')}
+        draggable
+      >
+        Output Node
+      </div>
+    </aside>
+  );
+};
+
+export default Sidebar;